Material handling equipment is used in many different industries, especially in manufacturing fields, including, without limitation, ship building, aerospace or plane building, automotive, heavy equipment, appliances, construction material, furniture, etc. As variety and volume of goods and materials that the equipment handles have been grown drastically in past few decades, needs for automating material handling processes in various industries span out even more demanding requirements on the machineries and equipments, including speed, precision, gentler handling of materials, etc.
Turntables alone have evolved significantly over the past few decades. In most of cases, pneumatic motor driven turntables are most commonly used equipment. This type of turntables is generally supported by air bearings or caster wheels and rotate around a centre hub. Usually, a friction wheel, driven by an air motor, is used to provide power to turn the table. The friction wheel is pressed against the side of the turntable, contacting with a ring, which is welded on the perimeter of the wheel for providing the friction surface. As the air motor is engaged to rotate the friction wheel, the friction wheel, in turn, rotates the turntable. Once the turntable reached to a designated position, a shot pin will be fired to stop and hold the turntable in the desired position.
There are a number of shortcomings with the current pneumatic motor driven turntables. First, they often create sudden movements, i.e. sudden start and sudden stop due to a shot pin fired to stop and hold the position. These sudden movements could cause problems if a material or materials placed on the turntable are sensitive to the shock. These sudden movements also create many constraints of where and how to place or stack materials on the turntable to avoid damages from sudden movements, load shifts, etc. Quite often, some supporting structures on this type of turntables are required to avoid the aforementioned problems; however, this will also add another constraint related to operable and available space. The sudden movement also causes faster pace of wear and tear, mechanical stresses and damages to the shot pins and friction wheel. As the friction wheel wears, it will worsen the driving efficiency of the turntable. Ultimately, it will cause the maintenance cost to rise.
Second, pneumatic motor driven turntables lack positioning accuracy due to the lack of precision in pneumatic motor friction wheel drive. Most of the pneumatic motor driven turntables with friction wheels have a position accuracy of about +/−1 inch or larger. Accuracy is a very crucial factor for automation application, especially for robot loading and picking applications. However, mainly, due to the inefficiency of friction wheel (error from wear and tear of a ring to provide friction surface, slippage, etc) and difficulty to control speed, acceleration and deceleration with the air motor, it is almost impossible to improve the positioning accuracy.
Third, pneumatic turntables are difficult to integrate and interface with an electric control system, since most of the moving parts are pneumatically driven. Solenoid valve may be used to control pressured air for starting and stopping the turntable by an electric control system. However, there is no cost effective solution to control speed for avoiding sudden movements and for improving positioning accuracy.
Forth, due to the physical packaging limitation, pneumatic drive motors are usually placed outside of the turntable frame structure, being exposed to the environment, especially, to dust, dirt or physical damages; therefore, it causes a high maintenance cost due to the exposure. It also becomes a constraint when considering for laying out floor plan, i.e. for a production line.
Fifth, due to the mechanical structure of pneumatically driven turntables and how it is driven through friction wheel, the shape of the turntables are generally limited to round and circle. This limits where and how the table is to be applied. Due to its circular construction, it is expensive to build as well.
Sixth, due to the complexity of and stresses to the mechanical structure and components of the pneumatically driven turntables, maintenance costs are quite high, plus cost for repairing air bearings and drive chain cannot be ignored, since various parts requires air tightness, and any loose parts, cracks, wear and tear would worsen the efficiency and, thus, productivity after all.
Lastly, due to the usage of highly pressured air for driving pneumatic motor, it often produces hazardous noise. It would become a health concern for the operators, and would indirectly cause productivity to be deteriorated.
The objective of the present invention is to address all these shortcomings from the aforementioned commonly used solution, and to provide better position accuracy, more suitable for automation, mechanically simpler, but yet, inexpensive to build and maintain.